Potassium currents are important for controlling the membrane potential and, therefore, the level of electrical activity in neurons, muscles and various other cell types. Although the physiological properties of K+ channels have been studied for a number of years, lack of either a rich tissue source or a good ligand has prevented the biochemical purification of any K+ channel. Using the genetic approach available in Drosophila, the first complete sequence for a K+ channel was recently reported from the Shaker locus of Drosophila. A homologous gene expressed in the mouse brain was subsequently cloned. Here we propose to extend our studies on the probable mouse-brain K+ channel gene, called MBK1. We will address the following specific aims: 1) To express physiologically the MBK1 cDNA, thereby confirming that it encodes a K+ channel component. 2) To study the function of residues that are conserved between Shaker and MBK1 using in vitro mutagenesis. 3) To characterize the MBK1 protein, including the channel of which it is likely to be a part. 4) To identify the tissues that express MBK1 and, within the brain, to localize MBK1 expression by in situ hybridization and the MBK1 protein using immunocytochemistry. 5) To characterize the MBK1 gene, its structure and regulatory elements. 6) To identify the chromosomal location of MBK1 and to determine if the MBK1 locus correlates to any behavioral mutants in mice. Answers from these studies may help to explain, at the molecular level, how membrane excitability is controlled and, in diseases like epilepsy, periodic paralysis or diabetes, how uncontrolled membrane excitability may come about.